The gun pictured in this article was built in 1981 according to the serial number, but wasn't bought new until 1987, and soon thereafter my father bought it from the original purchaser. Dad soon named the gun Snuffy, after Snuffy Smith of comic strip fame.
This revolver is built on a K frame (S&W refers to their frame sizes by letter) and has a square butt (grip frame). Round butt versions of the 66 were also made.
Barrel length of the pictured gun is 4 inches, but the 66 was offered with 2.5", 3", 4" and 6" barrel lengths at different times.
The Model 66 is a double-action six-shot revolver, and the pictured gun has a red ramp front sight (sight is built integral with barrel and has a red plastic insert), and adjustable rear sight.
This particular revolver has a standard trigger with vertical grooves, while the "target trigger" is supposed to be 0.4" wide and serrated. The hammer is standard, but still plenty hefty and well-textured. A S&W target hammer (TH) should have a spur that's 1/2" wide.
Stamped on the left side of this gun are the words "SMITH & WESSON" along the barrel, with the S&W trademark logo on the frame below the cylinder latch.